What was found
(CAN) BRAKE TEMP INDICATION APPEARS TO BE INDICATING CORRECTLY. ON ARRIVAL NR 1 BRAKE WAS FOUND COLD TO THE TOUCH AND NR 2 WAS SUBSTANTIALLY HOTTER. TAXI TEST REQUIRED TO VERIFY ANY CHANGE IN BRAKING AND TEMP INDICATIONS. GROUND TAXI TEST CARRIED OUT. NR 1 BRAKE STILL NOT ACTUATING PROPERLY. ONGOING TROUBLESHOOTING FOR DEFECT OF NR 2 BRAKE ASSY RUNNING HOTTER THAN THE REST OF THE BRAKES. FOUND DURING TROUBLESHOOTING THAT THE LOWER BRAKE CONTROL VALVE PISTON SUPPLYING HYD. PRESSURE TO NR 1 BRAKE HAD FAILED INTERNALLY -EITHER BROKEN PISTON/SPRING INSIDE BRAKE CONTROL VALVE - ONLY ALLOWING MINIMAL PRESSURE TO NR 1 BRAKE. LOWER BRAKE CONTROL VALVE REPLACED DUE TO PISTON UNSERVICEABLE (NR 1 BRAKE). LOWER BRAKE CONTROL VALVE REPLACED IAW CRJ200 AMM 32-43-06 PG 401 - PG 413. TAXI TEST COMPLETED. NO FURTHER FAULTS NOTED.